IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


V 


// 


{•/ 


.^      #^ 


<       ^°.    '^^ 


&,. 


V 


A. 


y^ 


1.0 


I.I 


!f-||IIM    i2.5 

'"  iliu 

2.0 


2.2 


1.8 


1.25 

1.4 

1.6 

< 

6"     — 

► 

V} 


9 


'<5. 


e. 


cri 


'm  a 


/a 


e^i- 


% 


9. 


o 


7 


V// 


M 


Photographic 

Sciences 
Corporation 


23  WEST  MAIN  STREET 

WEBSTER,  NY.  14580 

(716)  872-4503 


MKl 


&X 


.^" 


y   c?o 


Q- 


CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  Institut  canadien  de  microreproductions  historiques 

1980 


Technical  and  Bibliographic  Notes/Notes  techniques  et  bibliographiques 


The  Institute  has  attempted  to  obtain  the  best 
original  copy  available  for  filming.  Features  of  this 
copy  which  may  be  bibliographically  unique, 
which  may  alter  any  of  the  images  in  the 
reproduction,  or  which  may  significantly  change 
the  usual  method  of  filming,  are  checked  below. 


L'Institut  a  microfilmd  le  meilleur  exemplaire 
qu'il  lui  a  6t6  possible  de  se  procurer.  Les  details 
de  cet  exemplaire  qui  sont  peut-§tre  uniques  du 
point  de  vue  bibliogruphique,  qui  peuvent  modifier 
une  image  reproduite,  ou  qui  peuvent  exiger  une 
modification  dans  la  mdthode  normale  de  filmage 
sont  indiqu6s  ci-dessous. 


□    Coloured  covers/ 
Couverture  de  couleur 


n 

D 
D 


n 


n 


Covers  damaged/ 
Couverture  endommagde 


Covers  restored  and/or  laminated/ 
Couverture  restaurde  et/ou  pelliculde 


Cover  title  missing/ 

Le  titre  de  couverture  manque 


□    Coloured  maps/ 
Cartes  g6ographiques  en  couleur 


Coloured  ink  (i.e.  other  than  blue  or  black)/ 
ere  de  couleur  (i.e.  autre  que  bleue  ou  noire) 


□    Coloured  plates  and/or  illustrations/ 
Planches  et/ou  illustrations  en  couleur 


Bound  with  other  material/ 
ReliS  avec  d'autres  documents 

Tight  binding  may  cause  shadows  or  distortion 
along  interior  margin/ 

La  reliure  serr^e  peut  causer  de  I'ombre  ou  de  ia 
distortion  le  long  de  la  marge  intdrieure 

Blank  leaves  added  during  restoration  may 
appear  within  the  text.  Whenever  possible,  thei;e 
have  been  omitted  from  filming/ 
II  se  peut  que  certaines  pages  blanches  ajoutdes 
lors  d'une  restauration  apparaissent  dans  le  texte, 
mais,  lorsque  cela  6tait  possible,  ces  pages  n'ont 
pas  6td  film^es. 


n 
c 
n 

n 


Coloured  pages/ 
Pages  de  couleur 

Pages  damaged/ 
Pages  endommag^es 

Pages  restored  and/or  laminated/ 
Pages  restaurdes  et/ou  pelliculdes 

Pages  discoloured,  stained  or  foxed/ 
Pages  d6color6es,  tachetdes  ou  piqudes 

Pages  detached/ 
Pages  d6tach6es 

Showthrough/ 
Transparence 

Quality  of  print  varies/ 
Quality  in^gale  de  I'impression 

Includes  supplementary  material/ 
Comprend  du  materiel  supplementaire 

Only  edition  available/ 
Seule  Edition  disponible 

Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  etc.,  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Les  pages  totalement  ou  partiellement 
obscurcies  par  un  feuillet  d'errata,  une  pelure, 
etc.,  ont  6t6  film^es  d  nouveau  de  fagon  d 
obtenir  la  meilleure  image  possible. 


D 


Additional  comments:/ 
Commentair'es  suppldmentaires; 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  filmd  au  taux  de  reduction  indiqud  ci-dessous. 


10X 

14X 

18X 

22X 

26X 

30X 

y 

12X 


16X 


20X 


24X 


28X 


32X 


The  copy  filmed  here  has  been  reproduced  thanks 
to  the  generosity  of: 

Library  of  the  Public 
Archives  of  Canada 

The  images  appearing  here  are  the  best  quality 
possible  considering  the  condition  and  legibility 
of  the  original  copy  and  in  keeping  with  the 
filming  contract  specifications. 


Original  copies  in  printed  paper  covers  are  filmed 
beginning  with  the  front  cover  and  ending  on 
the  last  page  with  a  printed  or  illustrated  impres- 
sion, or  the  back  cover  when  appropriate.  All 
other  original  copies  are  filmed  beginning  on  the 
first  page  with  a  printed  or  illustrated  impres- 
sion, and  ending  on  the  last  page  with  a  printed 
or  illustrated  impression. 


The  last  recorded  frame  on  each  microfiche 
shall  contain  the  symbol  •— »>  (meaning  "CON- 
TINUED"), or  the  symbol  V  (meaning  "END"), 
whichever  applies. 


L'exemplaire  film6  fut  reproduit  grdce  d  la 
u^n6rosit6  de: 

La  bibliothdque  des  Archives 
publiques  du  Canada 

Les  images  suivantes  ont  6t6  reproduites  avec  le 
plus  grand  soin,  compte  tenu  de  la  condition  et 
de  la  nettetd  de  l'exemplaire  film6,  et  en 
conformity  avec  les  conditions  du  contrat  de 
filmage. 

Les  exemplaires  originaux  dont  la  couverture  en 
panier  est  imprimis  sont  filmds  en  commenpant 
par  le  premier  plat  et  en  terminant  soit  par  la 
dernidre  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration,  soit  par  le  second 
plat,  salon  le  cas.  Tous  Ses  autres  exemplaires 
originaux  sont  film^s  en  commen9ant  par  la 
premidre  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration  et  en  terminant  par 
la  dernidre  page  qui  comporte  une  telle 
empreinte. 

Un  des  symboles  suivants  appart  Ttra  sui  la 
dernidre  image  de  cheque  microfiche,  selon  le 
cas:  le  symbols  —^  signifie  "A  SUIVRE",  le 
symbols  V  signifie  "FIN". 


Maps,  plates,  charts,  etc.,  may  be  filmed  at 
different  reduction  ratios.  Those  too  large  to  be 
entirely  included  in  one  exposure  are  filmed 
beginning  in  the  upper  left  hand  corner,  left  to 
right  and  top  to  bottom,  as  many  frames  as 
required.  The  following  diagrams  illustrate  the 
method: 


Les  cartes,  planches,  tableaux,  etc.,  peuvent  dtre 
fiimds  d  des  taux  de  reduction  diffd'ents. 
Lorsque  le  document  est  trop  grand  pour  dtre 
reproduit  en  un  seul  cliche,  il  est  fiimd  d  partir 
de  Tangle  sup6rieur  gauche,  de  gauche  d  droite, 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'images  n6cessaire.  Les  diagrammes  suivants 
illustrent  la  m6thode. 


1 

2 

3 

1 

2 

3 

4 

5 

6 

c 


Fro 


T 


CURRENTS  OF  AIR  AND  OCEAN 


l\ 


CONNECTION  WITH  CLIMATES, 


Regions  of  Summer  Rains  and  Summer  Droughts. 


BT 


J.  BEAUFORT  IIURTJUIRT,  LL.  D., 
OF  OTTAWA,  CANADA. 


From  the  PuocEEDiNos  of  tiik  Ameiucan  AssoriATioN  for  the  Advancement 
OF  SCIENCE,  Vol.  XXXI,  iMontrciil  Meeting,  August,  1882. 


PRINTED    AT    THE    SALEM    PRESS, 

SALEM,  MASS. 
1883. 


tu 

CO 

in 

tv\ 

tei 

tli( 

be 

up 

su 

va 

or 

ail 

CURRENTS    OF    AIR    AND    OCEAN  ;    BY   J.    b.    HURLBERT. 


367 


Currents  of  Air  and  Ocean  in  connection  with  Climates, 
Regions  of  Summer  Rains  and  Summer  Droughts.  By  J. 
Beaufort  IIurerert,  of  Ottawa,  Canada. 

lABSTUACT] 

The  prevailing  winds  in  the  north  temperate  zone  are  from 
southwest  towards  the  nortlieast.  This  great  ciu'ient  of  air  may 
be  said  to  he  constant  north  of  latitude  85°.  In  the  upper  roaion 
of  the  air  it  blows  nearly  every  day  in  the  year  from  some  point 
near  the  southwest  towards  the  northeast.  With  a  constant 
movement  of  the  air  in  high  altitudes  from  the  southwest  there 
must  be  a  return  current  from  the  north  towards  the  southwest,  as 
there  are  counter  cnirents  in  tiie  ocean  ;  but  these  polar  winds 
near  the  surface  of  the  earth  blow  from  all  the  colder  points  of  the 
compass. 

The  warm  currents  of  air  and  water  falling  upon  westein  coasts, 
and  aerial  currents  passing  over  the  continents,  elevate  the  tem- 
l)eratures  of  the  western  parts  of  the  continents,  while  the  cold 
cu'-rents  pressing  upon  eastern  shores  lower  the  temperatures 
tlicre. 

The  mean  temperature  of  the  Gulf  stream  in  the  Gulf  of  Mexico 
is  80°  Fahrenheit ;  its  maximum  temperature  is  86°,  or  5)°  al)ove 
the  ocean  temperature  due  the  latitude.  Increasing  its  latitude 
10°,  it  loses  two  degrees  of  heat,  and  after  running  3,000  miles 
towards  the  north  still  preserves  the  temperature  of  summer. 
With  this  temperature  it  crosses  the  fortieth  degree  of  north  lati- 
tude, and  cpreading  out  for  thousands  of  square  leagues  over  the 
cold  waters  of  the  ocean,  does  much  to  mitigate  the  rigors  of  winter 
in  Europe.  When  it  strikes  the  British  islands  it  divides  into 
two  parts,  the  main  current  going  to  the  I'olar  sea,  the  other  en- 
tering the  Bay  of  Bi.>icay. 

It  has  been  estimated  that  tlie  quantity  of  heat  discliarged  over 
the  Atlantic,  from  the  waters  of  tlio  Gulf  streau)  in  winter,  would 
be  sufficient  to  raise  the  whole  column  of  atniosijhere  which  rests 
upon  France  and  the  British  islands  from  the  freezing  j)oint  to 
summer  heat.  Every  western  wind  which  blows  (and  the  pre- 
vailing winds  are  from  the  west  or  from  some  {)oint  near  the  west 
or  southwest  in  this  part  of  the  ocean)  crosses  the  Gulf  stream 
and  carries  with  it  a  i)ortion  of  its  heat,  discharging  it  in  its  pas- 


3G8 


CURRENTS    OF    AIR   AND    OCKAN  ; 


sao-e  ovor  Europe.  Tlie  isotlierm.il  linos  of  60°  tind  55°,  starting 
from  the  parallel  of  40°  on  the  American  coast,  run  in  a  north- 
easterly direction,  retaining  nearly  the  same  oceanic  temperature 
on  the  European  side  in  latitude  55°  and  60°  as  exists  on  the 
American  coast  in  latitude  40°. 

In  the  Pacific  there  are  tropic  and  arctic  currents  like  those  in 
the  Atlantic,  and  from  similar  causes.  The  Japan  stream,  or 
Kuro-Sivvo  — black  stream  —  a  name  derived  from  the  deep  blue 
color  of  its  waters,  flows  from  the  southeast  of  Asia  in  a  north- 
easterly direction,  falling  upon  the  western  coast  of  North  Amer- 
ica. This  stream,  flowing  many  thousand  miles  further  than  the 
Atlantic  tropic  ciwrent,  is  not  so  hot  nor  its  littoral  waters  so 
cold  as  those  in  the  Atlantic,  but  it  spreads  over  the  entire  racific 
coast  (^f  Canada.  These  two  currents  in  the  Pacific  — the  arctic 
and  tropical  —  produce  similar  effects  to  those  in  the  Atlantic; 
the  one  warming  the  western  coast  of  North  America,  in  high 
latitudes,  and  the  other  cooling  the  eastern  shores  of  Asia. 

Through  the  agency  of  these  two  cuirents  in  the  Atlantic,  the 
western  countries  of  En  rope  are  much  warmer  than  the  eastern 
parts  of  America  in  simiUsr  latitudes ;  the  difference  being  about 
eight  degrees  in  latitude  41°  ;  eleven  and  a  half  in  latitude  51°; 
and  twenty-five  in  latitude  58°.  Similar  causes  in  operation  in 
the  Pacific  ocean  give  an  equal  elevation  of  the  temperature  of  the 
western  coasts  of  America  over  the  eastern  coasts  of  Asia  in  the 
same  latitudes  — the  arctic  currents  chilling  the  one  and  the  tropi- 
cal currents  warming  the  other. 

From  Vancouver  in  latitude  49°  to  Sitka  in  57°,  the  summer  tem- 
peratures are  as  high  and  as  uniform  as  in  the  west  of  Europe, 
ex'-ept  where  the  vicinity  of  mountains  may  modify  the  normal 
conditions  of  climate.  Sir  John  Kicliardson  says  "  the  climate  of 
Sitka"  (on  the  Pacific  coast)  "  is  much  warmer  than  that  of  Eu- 
rope in  the  same  parallel"  (Arc.  Ex.,  Vol.  II,  p.  279). 

The  isothermal  of  G0°  for  the  three  summer  months  rises  as  high 
as  latitude  68°  east  of  the  Rocky  mountains  in  the  valley  of  Mac- 
kenzie river.  Youkon,  west  of  Mackenzie  river  and  within  the 
Arctic  circle,  latitude  67°,  has  a  July  65°   7',  and  an   August  of 

60°. 

In  comparing  the  well  known  regions  of  the  old  world  with  the 
less  known  corresponding  parts  ol"  the  new,  western  coasts  with 
western,  eastern  with  eastern,  and  interior  divisions  with  interior, 


> 


BY   .1.  BEAUFOUT    HURLBEUT. 


3fi9 


starting 
a  nortli- 
perature 
3  on  the 

thoKO,  in 
ream,  or 
eep  blue 
a  iiorth- 
th  Anier- 
thau  tlie 
,uters  so 
e  Tacilic 
he  arctic 
\.thintic ; 
,  in  higli 
a. 

mtic,  the 
e  eastern 
ng  about 
ude  51° ; 
ration  in 
ire  of  the 
ia  in  the 
tlie  tropi- 

imer  tein- 
Europe, 
e  normal 
;limate  of 
it  of  Eu- 

^s  as  high 
y  of  Mac - 
(ithin  the 
August  of 

with  the 
asl.s  vvitii 
1  interior, 


we  iiiid  a  remarlvul)le  similarity  in  the  climates  of  the  two  conti- 
nents. Canton,  in  China,  latitude  23°,  has  a  summer  tempei-ature 
of  82°,  and  Key  West,  in  Florida,  latitude  24°,  32',  a  summer  of 
82°.  Pekin,  latitude  40°,  has  a  summer  of  70,°  which  is  only  two 
or  three  degrees  above  that  of  l'liiladel|)hia  of  the  same  latitude. 
JNIangas-aka,  Japan,  and  Charleston,  South  Caiolina,  in  the  same 
latitudes,  have  summers  of  80°.  London,  in  the  west  of  Europe, 
and  Vancouver,  in  the  west  of  North  America,  in  similar  lati- 
tudes, have  the  same  mean  summei  temperatures,  about  6H°  ; 
Sitka,  in  latitude  57°,  Sir  .John  liichardson  says,  has  a  climate 
nnich  warmei'  than  Europe  in  the  same  latitude. 

The  climates  of  the  interior  are  warmer  in  sunnner  and  colder 
in  winter  than  those  on  eastern  and  western  coasts,  but  are  some- 
what similar  on  both  continents,  being,  however,  warmer  on  the 
Red,  Saskatchewan,  and  Mackenzie  rivers,  than  in  the  same  par- 
allels on  the  eastern  continent.  The  isothermal  of  65°,  for  the 
three  summer  months,  crosses  the  lied  river  ir  latitude  50°,  and 
rises  on  liie  Mackenzie  to  latitude  60°. 

The  summer  rains,  too,  throughout  Canada,  are  similar  to  those 
in  Euiope  in  the  same  latitudes  from  the  Mediterranean  to  the 
Arctic,  being  somewhat  uniform  during  the  agricultural  months, 
l)ut  more  cop.ous  in  Canada. 

South  of  the  boumlary  between  Canada  and  the  United  States, 
west  of  the  Mississippi,  are  the  areas  of  summer  droughts  —  a 
rainless,  treeless  region,  similar  in  position  on  this  continent,  and 
in  the  character  of  the  country  to  the  desert  areas  of  the  old 
world  —  the  one  beginning  on  the  western  coasts  of  Mexico  and 
California,  and  extending  to  liritish  America  on  the  north,  and 
over  half  the  continent  eastward  ;  the  other  beginning  on  the 
western  coast  of  Africa  near  the  same  latitude  as  the  American 
desert,  and  extending  northeast waid  or  east  by  north  over  Africa, 
Palestine,  Independent  Tartary  and  Manshire  Tartary,  nine  thou- 
sand miles  in  the  direction  of  the  i)revailing  winds. 

That  portion  of  the  North  American  continent  extending  from 
the  Atlantic  westward  more  than  2,000  miles  in  the  latitude  of 
Canada,  and  from  the  Gulf  of  Mexico  for  1,500  miles  northward, 
is  covered  with  a  mixed  foiest  of  conifene  and  deciduous  trees, 
which  is  unparalleled  in  exleiil,  and  in  the  variety  and  value  of  its 
woods. 

These  forests,   so  beautiful  and   grand  in  their  primitive  state, 


370 


CURUKNTS    OK    Allt    AND    OCEAN  ; 


have  a  valuo  qviito  indopciidoiit  of  their  inoiioy  worth.  Tliey 
have  a  most  poworiul  and  favorable  iiilliience  upon  the  climates  of 
the  country,  cheek  evaporation,  and  keep  the  water  Ioniser  in  the 
soil,  thus  supplying  the  roots  of  plants,  feeding  tin  springs  and 
streams,  etc. 

West  of  this  vast  forest,  south  of  the  parnllel  of  48°  or  49°,  is 
the  treeless  region.  The  INIississippi  may  he  taken  as  near  the 
boundary  of  these  two  zones  marked  with  such  different  features, 
the  forest  in  many  places  not  reaching  that  river,  in  others  ex- 
tending beyond  it,  and  again  reappearing  on  tlie  l'a.!ilic  coast. 
East  of  the  Mississippi  trees  appear  first  along  tlie  water-courses 
and  on  soil--,  retentive  of  moisture,  being  still  abscjit  on  the  up- 
lands and  sandy  plains.  To  the  north  this  immense  treeless  re- 
gion runs,  in  the  country  of  the  Upiier  INIissonri  (longitude  110° 
west),  north  of  latitude  50°.  Tlirotighout  these  immense  areas 
there  is  either  a  total  absence  of  rain  in  summer,  as  in  the  desert 
parts,  or  an  insuHu!iency,  as  on  the  prairies.  The  grnsses  which 
cover  parts  of  these  (hy  up  in  sunnner,  but  their  roots,  Ibrming  a 
deep  matted  sod,  have  vitality  enough  to  put  forth  fresh  shoots 
under  the  rains  of  spring  and  autumn  ;  trees,  however,  which  are 
withered  up  by  the  droughts  and  arid  winds  of  summer,  have  no 
such  vitality. 

Vast  portions  of  America,  Africa,  Asia  and  Australi;i,  are  des- 
titute of  trees,  while  other  equally  extensive  regions  are  covered 
with  forests.  These  treeless  zones  lie  in  similar  positions  on  the 
continents,  beginning  near  the  same  latitudes  on  the  westcu'ii 
coasts  and  running  northeastward  in  the  northern  hemisphere, 
and  southeastward  in  the  southern,  in  the  direction  of  the  pre- 
vailing winds. 

In  the  OKI  World  (for  Europe,  Asia  and  Africa  nmst,  on  the 
question  of  climates,  be  taken  as  one  body  of  land)  these  treeless 
and  mainly  desert  regions  begin  on  the  west  coast  of  Africa,  north 
of  the  twentieth  parallel,  and  run  northeastward  or  east  by  north, 
9,000  miles  over  Africa,  Palestine,  noi-thern  Aral)ia,  and  Inde- 
pendent Tartary  to  latitude  r)0°  in  Mongolia,  ending  in  the  great 
desert  of  Gobi  or  ]\Ianshire  Tartary. 

In  North  America  we  have  a  similar  desert-treeless  region,  be- 
o;inninff  in  old  and  new  California  and  on  the  coasts  of  Mexico 
(in  the  same  latitudes  as  the  African  desert),  and  extending  to 
the  l\[ississii»[)i  and  beyond  it,  on  the  east,  and  to  JJritisii  America 


HV    J.   BKAUKOItT   IIUKLBEKT. 


371 


111.  They 
(Oimatos  of 
i<(or  in  the 
[)rings  and 

°  or  49°,  is 
s  near  the 
it  features, 

otlicrs  ex- 
cidc  coast, 
ter-courses 
on  the  II p- 
tieeless  re- 
ritnde  110° 
ense  areas 

the  desert 
sses  which 

rorniiiiji  a 
esh    shoots 

wiiich  are 
T,  liave  no 

ii,  are  des- 
ire covered 
ons  on  the 
le  western 
leinisphere, 
ol'  the  pre- 

ust,  on  the 
L'se  treeless 
frica,  north 
t  by  north, 
and  Inde- 
i  the  great 

region,  be- 

of  Mexico 

[tending  to 

■i\\  America 


on  the  north.  The  winds  over  tliese  desert  areas  on  both  conti- 
nents blow  almost  invariably  in  summer  from  some  point  near  the 
southwest  towards  the  northeast.  These  portions  of  the  continents 
are  destitute  mainly  of  summer  rains,  but  have  high  summer  tem- 
peratures. Upon  the  modifications  caused  in  these  desert  areas 
by  the  high  lands  of  Mexico  and  the  vast  Mediterranean  sea  we 
cannot  here  enter,  but  may  merely  state  that  the  mountains  of 
Mexico  limit  the  deserts  there,  and  that  great  sea  north  of  Africa 
causes  a  more  humid  air  in  the  south  of  Europe  and  limits  the 
deserts  in  that  direction  ;  yet  Spain,  Italy,  Sicily,  and  the  whole 
country  nortlieastward  into  Hungary,  frequently  suffer  from  sum- 
int  V  droughts. 

The  reason,  as  a  permanent  cause,  often  assigned  for  these  por- 
tions of  the  continent  being  destitute  of  trees— namely,  the  prairie 
fires  —  cannot  for  a  moment  bear  investigation. 

Fires  were  naturally  suggested  to  the  first  rude  settlers,  to 
whom  the  evidence  of  sight  is  the  chief  guide,  as  the  only  cause. 
In  many  parts  of  the  African,  Asiatic  and  American  deserts  and 
prairies  there  are  no  fires,  still  they  are  treeless.  In  other  coun- 
tries, fires  are  as  frequent  where  forests  are  iiernianeh,  or,  if 
burned  down,  young  trees  immediately  grow  up  again.  The  ex- 
istence of  forests  over  a  region  2,000  miles  by  1,000,  and  their 
failure  where,  anrl  onh/  where,  the  summer  rains  fail  and  the  arid 
winds  prevail,  ought  to  have  suggested  the  exi)lanation. 

That  the  prairie  fires  sweeping  over  exten<led  areas  may  have 
kept  trees  from  s6me  localities,  near  rivers  or  on  retentive  soils,  is 
possible ;  but  such  exceptions,  limited  and  local,  have  no  wei<'ht 
in  opiiosition  to  the  fact  that  millions  of  square  miles  have  re- 
mained, through  all  the  a<>es  of  history,  desert  and  treeless  on  the 
borders  of  other  equally  extensive  areas  covered  vvitli  dense  for- 
ests. The  climates  which  have  produced  these  two  distinct  re- 
sults over  those  regions  have  remained  permanent  for  ages,  and 
will  remain  permanent  in  the  future,  unless  changes  supervene  in 
the  entire  solar  system  ;  Init  for  the  calculation  of  such  imaginary 
phenomena  astronomy  furnishes  no  data.  We  may  infer,  there- 
fore, that  those  conditions  of  climate  —  heat  and  humidity  in  the 
one  case,  and  heat  and  aridity  in  the  other  —  remaining  the  same, 
their  etfects  —  forests  and  treeless  regions  —  will  be  permanent 
expressions  of  those  fixed  efficient  causes. 

The  attempts  to  account   for  the  deserts  of  the  Old  and  New 


872 


CURRKNTS    OF    AIR   AND    OCKAN  ;    BY    J.    B.    IIURI-BKRT. 


World  by  the  physical  conligtinition  of  tho  continents,  have  led  to 
many  ingenious  thcorios.  The  chief  of  tliese  is  the  jisstunption 
tliiit  nionnliiiii  cli.'iins  to  tlie  west  of  those  rtiinless  regions  con- 
dense the  vapor  brought  in  the  southwest  winds,  causing  lieavy 
rains  on  the  western  sides  of  tiie  mountains,  but  leaving  the 
winds  without  vapor  east  of  these  mountain  chains.  The  phe- 
nomena of  rain  on  the  west,  but  none  on  the  east  of  the  Ghauts 
in  Ilindostan  and  other  places,  have  been  taken  as  suiHcient  bases 
for  tiiis  theory. 

Tliat  those  regions  having  no  summer  rains  are  on  similar  parts 
of  the  continents  north  and  south  of  tlie  equator,  both  in  the 
eastern  and  western  hemispheres,  beginning  on  western  coasts  at 
about  the  same  latitudes ;  that  there  are  no  mountains  west  of 
tiie  Desert  of  Saliara,  and  the  rainless  regions  in  Australia;  that 
the  entire  coasts  of  Mexico,  old  and  new  California,  west  of  the 
mountains,  are  quite  as  destitute  of  rain  in  summer  as  the  regions 
east ;  tiiat  those  west  winds  give  heavy  falls  of  rain  to  the  north 
and  northeast  tliroughout  Canada,  and  in  autumn,  winter,  and 
early  spring,  deposit  lieavy  rain  and  snow  on  tiiose  interior  desert 
areas  cast  of  tlie  Rocky  mountains,  over  which  they  are  said  to 
pass  in  summer,  devoid  of  vapor, —  these  and  other  facts  ought  to 
have  corrected  the  erroneous  opinions  on  this  subject. 

That  the  great  southwest  currents  of  air  —  the  tropical  currents 

bring  the  vapor  which  falls  in  rain  and  snow,  is  here  assumed  as 

admitted,  for  it  is  the  basis  of  tiie   theory  which  we  are  contro- 
verting. 

Those  vast  wastes  are,  at  the  season  of  the  year  when  little  or 
no  rain  falls,  highly  heated  by  the  summer  suns.  The  southwest 
winds  passing  over  these  become  rarelied,  and  thus,  being  capable 
of  sustaining  even  more  vapor  than  at  a  lower  temperature,  retain 
the  humidity  with  which  they  have  come  from  the  tropics  so 
heavily  charged,  till  they  reach  the  cooler  regions,  north  and 
northeast,  where  they  are  condensed  into  rain  or  snow.  Hence  in 
summer  the  line  dividing  the  zones  of  rain  from  those  of  drought 
is  farther  to  the  northeast ;  as  autumn  and  winter  approach,  those 
highly  heated  plains  gradually  cool  suillciently  to  condense  the 
vapors  in  the  southwest  winds,  which  now  give  heavy  depositions 
of  rain  and  snow. 


nv. 

liiive  led  to 
[issiiinption 
?gioii9  eon- 
si  ii<j  lie.ivy 
leaving  the 
The  phe- 
tiie  Glwuits 
ieient  bases 

imiliir  parts 
both  in  the 
n  coasts  at 
ins  west  of 
tralia ;  that 
west  of  tlie 

the  regions 
,o  the  north 
winter,  and 
erior  desert 

are  said  to 
cts  ought  to 

cal  currents 

!  assumed  as 

are  contro- 


len  little  or 
le  southwest 
3ing  capable 
ature,  retain 
e  tropics  so 
,  north  and 
'.  Hence  in 
3  of  drouglit 
)roach,  those 
ondense  the 
depositions 


